Move enabled experimental feature to libutil struct

This is needed in subsequent commits to allow the settings and CLI args
infrastructure itself to read this setting.

src/libstore/globals.hh

@@ -3,7 +3,6 @@
 #include "types.hh"
 #include "config.hh"
 #include "util.hh"
-#include "experimental-features.hh"
 
 #include <map>
 #include <limits>
@@ -932,13 +931,6 @@ public:
           are loaded as plugins (non-recursively).
         )"};
 
-    Setting<std::set<ExperimentalFeature>> experimentalFeatures{this, {}, "experimental-features",
-        "Experimental Nix features to enable."};
-
-    bool isExperimentalFeatureEnabled(const ExperimentalFeature &);
-
-    void requireExperimentalFeature(const ExperimentalFeature &);
-
     Setting<size_t> narBufferSize{this, 32 * 1024 * 1024, "nar-buffer-size",
         "Maximum size of NARs before spilling them to disk."};